This invention relates generally to circuits for monitoring the capacitor battery of a direct current transmission line filter circuit, and more particularly to circuits for determining whether one or more capacitors in a capacitor battery having at least two parallel legs, each with a plurality of capacitors connected in series, have failed.
It is highly desirable in the operation of transmission lines which carry direct current produced by the rectification of alternating currents, to remove the harmonic frequency signal components which are superimposed on the direct current signal. Such harmonics are generally removed from the transmission line by filter circuits consisting of capacitive, inductive and resistive components. In direct current transmission systems which handle high voltages, the capacitive filter component usually consists of a plurality of individual capacitors which are arranged in a capacitor battery having at least two parallel legs, each with a number of capacitors connected in series. In such an arrangement, the failure of one capacitor in the capacitor battery will detune the circuit, but will not affect the total current flowing through the capacitor battery sufficiently to be detectable by measurement of the total current flowing through the capacitor bank. Since the harmonic currents flowing through the capacitor bank range in amplitude by a factor of approximately 100, depending upon the control angle of the rectifier, it would be extremely difficult to measure the widely varying current and determine whether a capacitor has failed.
It is a further problem in filter circuits which contain a large number of capacitors in a capacitor bank that variations in current resulting from the effect of temperature are larger than the current changes caused by the failure of one, or several, capacitors. Thus, even if the electrical characteristics of a transmission line and the control angle of the rectifier were known, the failure of a capacitor in the capacitor bank is not determinable only by measurement of the total current flowing through the capacitor bank.
Accordingly, it is an object of this invention to provide a circuit for monitoring a capacitor bank and reliably determining whether one or more capacitors have failed.
It is a further object of this invention to provide a circuit for determining whether one or more capacitors in a capacitor bank have failed by a measurement of the currents flowing through the capacitor bank.